Looking at it closely, it looks like the sand crabs we caught on the beaches in Alabama? It is eating the dying algae on the new rock and sand (wish I had 3 more at the moment) , I figured that when it cycles he probably wont make it. Tangirl- we were extremely careful, otherwise we would never had seen him tucked in the small hole he was hiding in. We debated for 10 min. whether to put him in....he started looking dead, so we put him in. There is nothing but lr in this tank, and he doesn't run away when we move sand around so he shouldn't be hard to catch (he he he). My husband thought maybe a fat worm fan, but there were no antenas. Hope your're right about the worm...man it was huge, then we lost sight of him ..